<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            width: 200px;
            height: 200px;
        }
        
        .box1 {
            position: relative;
            background-color: blanchedalmond;
            z-index: 9999;
        }
        
        .box1-son1 {
            position: relative;
            width: 100px;
            height: 100px;
            margin: auto;
            background-color: #ccc;
        }
        
        .box1-son2 {
            position: relative;
            width: 100px;
            height: 100px;
            margin: auto;
            z-index: -1;
            background-color: red;
        }
    </style>
</head>

<body>
    <div class="box1">
        盒子1
        <div class="box1-son1">
            盒子1的子盒子1
        </div>
        <div class="box1-son2">
            盒子1的子盒子2
        </div>
    </div>
</body>

</html>